Field of the Invention
The invention relates to an inverter stage including an npn transistor having a base terminal to which an input signal can be applied, a collector terminal at which an output signal can be picked up, and an emitter terminal connected through a controllable current source to a reference potential.
Such inverter stages are used particularly in a voltage controlled oscillator (VCO). Such VCOs serve to generate a clock signal having a frequency which can be adjusted by means of an externally applicable voltage. Typically, the VCO is an element in a so-called PLL (phase-locked loop).
In principle, there are two types of such VCOs, namely RC oscillators having a change in frequency which results from a change in stroke, and ring oscillators having a change in frequency that is effected by changing a gate transit time. That is very difficult to achieve with an RC oscillator, particularly if high frequencies are needed. Although ring oscillators enable very high frequencies, nevertheless the frequency range is relatively narrow.